The present invention relates to semiconductor packages, and more particularly, to a semiconductor package assembly that provides a true die to external fiber optic cable connection.
Most computer and communication networks today rely on copper wiring to transmit data between nodes in the network. Since the data transmitted over the copper wire and the data processed within the nodes are both represented in the form of electrical signals, the transfer of data at the node-copper wire interface is straight forward. Other than perhaps a level shift and signal amplification, no other signal processing is required for data transmitted over the copper wire to be decoded by the node. The drawback with using copper wire is its relatively low bandwidth. Copper""s ability to transmit data is significantly limited compared to other mediums, such as fiber optics. Accordingly much of the computer and communication networks being built today, including the Internet, are using fiber optic cabling instead of copper wire.
With fiber optic cabling, data is transmitted using light signals, not electrical signals. For example, a logical one may be represented by a light pulse of a specific duration and a logical zero may be represented by the absence of a light pulse for the same duration. In addition, it is also possible to transmit at the same time multiple colors of light over a single strand of optic fiber, with each color of light representing a distinct data stream. Since light is attenuated less in fiber than electrons traveling through copper, and multiple data streams can be transmitted at one time, the bandwidth of optic fiber is significantly greater than copper.
While fiber optic cabling is very efficient for transferring data, the use of light signals to process data is still very difficult. Data is typically transferred and stored in various locations before, during and after it is operated on in a computer. There still is no efficient way to xe2x80x9cstorexe2x80x9d light signals representative of data. Networks will therefore likely continue using fiber optics for transmitting data between nodes and silicon chips to process the data within the nodes for the foreseeable future. The interface between the fiber optic cable and the nodes that process the data is therefore problematic because signals need to be converted between the electrical and the light domains.
Fiber optic transceivers, which convert light signals from a fiber optic cable into electrical signals, and vice versa, are used as the interface between a fiber optic line and a computer node. A typical transceiver includes a substrate, grooves etched in the substrate to receive the individual fiber optic strands, one or more semiconductor devices mounted on the substrate, one or more discrete optical detectors for converting light signals received over the fiber optic cables into electrical signals, one or more discrete optical emitters for converting electrical signals from the semiconductor devices into light signals. A number of fiber optic transceivers are commercially available from Hewlett Packard, AMP, Sumitomo, Nortel and Siemens. The problem with all of these fiber optic transceivers is that they are expensive and difficult to fabricate. With each transceiver, the semiconductor devices, emitters, and optical detectors have to be individually mounted onto the substrate, which is a costly and time consuming process. This limits the applications in which optical interconnects could be substituted for traditional copper usage. Furthermore the use of discrete emitters and optical detectors adversely affects the performance of the transceiver because electrical parasitics between discrete components are sources of electrical attenuation of inter-chip signals at Gigabit per second speeds that are generally used with such transceivers, more power is consumed for driving these traces than would not be needed for an integrated device. The form factor of the on-board optical transceiver is relatively large and therefore does not facilitate inter-board and chip-to-chip optical interconnectability.
A low cost semiconductor device that provides a true die to external fiber optic connection is therefore needed.
The present invention provides a technique for manufacturing a low cost device that provides a true die to external fiber optic connection. Specifically, the present invention relates to several techniques for joining an optical device package to a semiconductor device package. The first technique involves using wirebond studs and an adhesive material, the second technique involves the use of an anisotropic conductive film, and the third technique involves the use of solder material. Each of these techniques provides high levels of thermal, electrical and optical performance. The methods apply to optical sub-assembly and chip sub-assembly interfaces in transceivers, transmitters, as well as receivers for opto-electronic packages.
One aspect of the present invention pertains to a method for attaching an optical device package to a semiconductor device package. This method includes forming a wirebond stud on an electrical contact surface located on a top surface of the semiconductor device package and applying an adhesive material to the wirebond stud. Then the optical device package is placed on top of the semiconductor device package such that an electrical contact surface on the optical device package makes contact with the wirebond stud and the adhesive material applied to the wirebond stud. Then the adhesive material is cured so that the optical device package is firmly attached to the semiconductor device package.
In another aspect of the present invention, a method for attaching an optical device package to a semiconductor device package involves forming a wirebond stud on an electrical contact surface located on a top surface of the semiconductor device package and applying an anisotropic conductive film to a bottom surface of the optical device package, which contains electrical contact surfaces. Then the bottom surface of the optical device package is placed onto the top surface of the semiconductor device package such that the electrical contact surfaces of the optical device package are aligned with the wirebond studs. And finally, pressure and heat are applied to the optical and the semiconductor device packages such that the wirebond stud sinks into the anisotropic conductive film and compresses the conductive particles together.
In yet another aspect of the present invention, a method for attaching an optical device package to a semiconductor device package involves applying a plurality of solder ball formations onto electrical contact surfaces located on a top surface of the semiconductor device package and placing a bottom surface of the optical device package onto the top surface of the semiconductor device package such that electrical contact surfaces on the bottom surface of the optical device package make contact with the solder ball formations.